Ship&#39;s propulsion plant



Nov. 8, 1966 T. B. HUTCHISON ETAL 3,283,506

SHIPS PROPULS ION PLANT Filed May 7, 1964 United States Patent 3,283,506 SHIPS PROPULSION PLANT Thomas Baird Hutchison, London, and Norman J. H. DArcy, Wallsend, England, assignors to Pametrada, Wallsend, England, and Esso Research and Engineering Co.,.Elizabeth, NJ.

Filed May 7, 1964, Ser. No. 365,603 Claims priority, application Great Britain, Sept. 26, 1963,

38,013/ 63 Y Claims. (Cl. 60-102) This invention relates to marine steam turbine propulsion installations.

It is usual in such installations to incorporate two or more main boilers which supply steam both to drive the main propulsion turbines and to provide certain auxiliary services. In oil .tankships, for example, the boilers are commonly designed to be capable of supplying considerably more steam than that required during normal full power operation at sea, the excess capacity being only used intermittently for such purposes as cargo heating and tank cleaning. Such an arrangement has a number of disadvantages: the pressure and temperature of the steam required to drive the main turbines efficiently is higher thanthat needed for the auxiliary services, the combination of the main and auxiliary duties resulting, therefore, in an unnecessarily high first cost of the boilers; the operation of the boilers considerably below their design output for the major part of their life is a wasteful use of expensive equipment and is prejudicial to economical boiler design; the operation of two or more boilers in parallel requires a complicated system of feed regulation and controls, anda high multiplication of expensive high pressure, high temperature steam piping. For the foregoing reasons, the reduction in operating costs which might be obtained by installation refinements such as the application of the well-known principle of reheat may be oifsetby a corresponding increase'in first cost and in any case do not mitigate the above disadvantages. v

The main object of the present invention is to provide a marine steam turbine propulsion installation particularly though not exclusively, for oil tankships inhibiting the above disadvantages and being expected to result in reductions in both first cost and operating cost compared with conventional installations.

The invention accordingly consists in a marine steam turbine propulsion installation of the kind in which a propeller is driven by steam from a boiler system supplying different steam-pressure conditions to stages of propulsion turbines, wherein a main boiler is provided for generating steam at high pressure for supply to the propulsion turbines, reheater means are provided bet-ween stages, and an auxiliary boiler is provided for generating steam at lower pressure for auxiliary purposes, e.g., tank cleaning, ballasting and deballasting, cargo heating etc.

Steam may be conveniently generated in the auxiliary boiler by passing high pressure steam from the main boiler through a heating coil in the auxiliary boiler by way of a closed circuit.

Reheating between an HP. propulsion turbine stage and an LP. propulsion turbine stage may be effected by providing reheater tubes in the main boiler over which flows a proportion of the combustion gases of the main boiler. To ensure that the reheater tubes are maintained at a safe low temperature even when there is no steam flowing through them, damper means may be arranged to close automatically when steam flow through the reheater tubes falls below a predetermined value.

The invention also consists in a marine steam turbine 3,283,506 Patented Nov. 8, 1966 propulsion installation comprising an HR turbine stage, an intermediate pressureturbine stage, an LP. turbine stage connected to a condenser, an H.P. reverse drive turbine stage and an LP. reverse drive turbine stage connected to a condenser, all of said turbine stages being coupled to one another and to a boiler feed pump, a propellerv shaft and an electric generator, a single main boiler for supplying steam either to said H.P. turbine stage, whence it passes by way of a reheat part of said boiler under control of a control damper to the intermediate pressure turbine stage and thence to a condenser by Way of said L.P. turbine stage, or to a condenser by way of said reverse drive turbine stages.

A standby electric generator, boiler feed pump and lubricating oil pump, driven by individual prime movers, may be provided to takeover the duties of these components during reverse drive and part-load operations.

The accompanying diagrammatic drawing illustrates one arrangement of installation in accordance With the present invention, in which a represents a single main high pressure steam generator, in which fuel is preferentially burnt in a single furnace. During ahead operation at full power, part of the combustion gases flow over the tubes of a superheater b from which steam is sup plied to a high pressure turbine or turbine stage 0. Exhaust steam from this turbine is returned to the boiler where its temperature is raised in the tubes of a reheater d over which flows another part of the combustion gases. Steam from the reheater is supplied to an intermediate pressure turbine or turbine stage e, from which exhaust steam flows to a low pressure turbine or tur-' binestage i and thence to a condenser g.

Auxiliary steam is generated at comparatively low pressure in an auxiliary steam generator p preferably disposed above the level of water in the steam drum of the main boiler a by internal tubes supplied in a closed circuit with high pressure steam from the boiler a. An auxiliary feed pump q is provided forthe boiler a.

The HR, LP. and LP. turbines or stages drive a propeller h through example, double reduction gearing i. In addition, the HP. turbine drives a main boiler feed pump 0 to which it is coupled mechanically, and a lubricating oil pump r and an electric generator through the reduction gearing i, this generator supplying the ships total electrical load during normal full power ahead operation at sea.. A standby lubricating oil pump s and electrical generator (not shown) are. also provided.

During astern operation and operation at part-power damper n on the gas outlet side of the reheater d is closed, the major part of the combustion gases being thereby caused to flow over the superheater tubes b, only a small proportion of the gases flowing over the reheater tubes d and superheater tubes .b'. The reheater tubes are thereby maintained at a safe low temperature even when no steam is flowing through them while the increased flow over tubes b compensates for the reduced heating by gas flowing over tubes b. This condition arises during astern operation, when the reheater is not used, steam from the superheater passing to the HP. astern turbine or stage, which may be structurally .an integral part of the LP. ahead turbine, and exhausting directly to the LP. astern turbine or stage, which may be structurally an integral part of the LP. ahead turbine and exhausting to the condenser.

The standby electrical generator and standby boiler feed pump q both driven by individual prime movers take over the duties of the corresponding main engine driven components during astern operation and part-load opera tion. These standby units may be arranged to come into operation "automatically when the rotational speed of the main engines falls below a predetermined fraction of the design full ahead speed. Similarly, the dampers causing the combustion gases to bypass the reheater may be arranged to close automatically when the steam flow through the reheater falls below a predetermined value.

Steam for auxiliary purposes other'than those connected with the operation of the main turbine machinery is generated at a relatively low pressure and temperature in either the steam generator p heated by steam from the main boiler, or in a separately fired auxiliary boiler. The relatively low pressure and temperature of this auxiliary steam permit its generation from water of relatively low purity compared with that required of the feed water for the main boiler, and the main and auxiliary feed systems are therefore isolated from one another during normal operation.

In oil tankships, the quantity of auxiliary steam required for certain purposes, such as domestic services and oil fuel heating is relatively small and in a preferred arrangement in this type of vessel, auxiliary steam for these purposes is supplied entirely from the steam generator p heated by steam from'the main boiler. The intermittent supply of steam required for cleaning the boiler tubes by soot blowing is also provided by this steam generator. The latter feature has the particular merit of using steam produced from the auxiliary feed water only, unlike conventional installations, in which steam for soot blowing is supplied directly from the main boiler and results in a total loss of an appreciable quantity of the highly purified water from the main feed system.

The larger quantities of auxiliary steam required in oil tankships for cargo heating and tank cleaning are .provided by a separately fired auxiliary boiler, which is designed to be capable of producing sufiicient steam for driving the main propulsion turbines at reduced power in the event of failure of the main boiler.

Another essential service to be provided in an oil tankship is a steam supply to drive the cargo oil pumps in harbour. This steam, in a conventional installation, is supplied from the main boilers. Whilst this steam could all be supplied by the single main boiler of the installation described, in a preferred arrangement the cargo pumping duty is shared between the main and auxiliary boilers, a proportion of the total pumping capacity thereby being available in the event of failure of one boiler or the other. I i

The first cost of an installation in accordance with the present invention compared with that of a conventional installation, is expected to be reduced as a result of:

(a) The use of only one main boiler.

(b) The use of reheat, of which a well known result is the reduction in the quantity of steam required to produce a given power, with a consequent reduction in boiler capacity and the .size of the main propulsion turbines. v

(c) The use of an auxiliary boiler to produce that steam for which hitherto a margin has been conventionally added to. the boiler capacity required for propulsion purposes only. I

(d) The simplification of the control'system compared with that required when operating boilers in parallel. The operating cost of such installation, compared .withthat of a conventional installation, is expected to be reduced as a result of:

(e) The use of reheat, the reduction in the quantity of steam required to produce a given power being accompanied by a corresponding reduction in the consumption of fuel.

*(f) The use of an electric generator and main feed pump driven by the main propulsion turbines which have a higher efiiciency than that of the smaller individual turbines commonly'used to drive the above units.

(g) The use of a single main boiler, as a result of which the simplification of the installation is expected to reduce the cost of maintenance.

There are also important operational advantages arising from the use of a single main boiler, as there are fewer valves and dampers to be operated during maneuvering. Consequently there are fewer opportunities for making mistakes, less time will be required for checking that no mistakes have been made, the machinery can respond more rapidly, and the chances of foolproof automatic operation are enhanced.

It also becomes more easy to provide for interlocks. For instance, it can be made impossible to reduce main ahead steam unless the reheat section has been made inoperative by closing the flue dampers.

There are also variations of this scheme which may be attractive. For instance the HP. astern .turbines can be structurally joined to the H.P. turbine instead of the LP. turbine, the LP. .turbinemay be joined to the LP. turbine or combined with the H.P. turbine. The power take off for the main boiler feed pump can be from the gear box, the various turbines instead of working in tandem as indicated in the diagram can be working in the usual way, each by means of a gear train into the main reduction gear.

By providing a main boiler installation and associated equipment of such design as to provide only the power necessary for ships propulsion with utilisation of reheat and by providing an auxiliary boiler for auxiliaryservices in accordance with the present invention, a substantial reduction in first costs and reduction in running costs is envisaged.

We claim: q

1. A marine steam turbine propulsion installation comprising a high pressure-turbine stage, an intermediate pressure turbine stage, a low pressure turbine stage, at least one reverse, drive turbine stage, a boiler including a reheater section, a condenser, conduits. to supply steam from the boiler selectively through an aheadflow path or an astern flow path to the condenser, the ahead flow path including the high pressure turbine stage, the reheater section, the intermediate pressure .tur bine stage and the low pressure turbine stage, the aster-n flow path including the or each reverse drive turbine stage the said turbine stages being mechanically connected .together, a propeller shaft, -a boiler feed pump and an electric generator being mechanically connected to the said turbine stages. p

2. An installation as claimed in claim 1, comprising damper means controlling the reheater section to prevent overheating thereof when the' steam is flowing in the astern path.

3. An installation as claimed in claim 2, comprising superheater tubes in the main boiler through which steam passes. to either, the ahead flow path or the,astern-fl0.W path, the superheater tubes being divided 'into two groups in series, exposed to different streams of the combustion gases of the main boiler, the reheater section comprising a set of reheater tubes exposed to that one of the said stream of combustion gases passing over the upstream,

with respect to the steam flow, and cooler. group of superheater tubes, the said damper means being elfec- .tive to substantially cut off the said stream of gases when the steam flow through the reheater tubes is reduced. 1 4. An installation as claimed in claiml, further comprising an auxiliaries steam generator for supplying steam at reduced pressure for auxiliary purposes.

5. An installation as claimed in claim 4, wherein the auxiliaries steam generator comprises a heating coil and conduits for passing "high-pressure steam in 'clos'edcircuit from the main boiler through the heating coil using natural circulation.

6. An installation as claimed in claim 1, further comprising a standby electric generator, boiler' feed pump,

and lubricating oil pump for use during reverse drive and part load operation.

7. An installation as claimed in claim 1, comprising a high pressure reverse drive turbine stage, and a low pressure reverse drive turbine stage.

8. An installation as claimed in claim 7, in Which the high pressure reverse drive turbine stage is structurally part of the intermediate pressure turbine stage and the low pressure reverse dr-ive turbine stage is structurally part of the low pressure turbine stage.

9. An installation as claimed in claim 1, in which the main boiler comprises only a single furnace.

10. An installation as claimed in claim 1, in which the intermediate pressure ahead turbine stage is housed in the same casing as one of the other ahead turbine stages.

MARTIN P. SCHWADRON, Primary Examiner.

ROBERT BUNEVICH, Examiner.

References Cited by the Examiner UNITED 

1. A MARINE STEAM TURBINE PROPULSION INSTALLATION COMPRISING A HIGH PRESSURE TURBINE STAGE, AN INTERMEDIATE PRESSURE TURBINE STAGE, A LOW PRESSURE TURBINE STAGE, AT LEAST ONE REVERSE DRIVE TURBINE STAGE, A BOILER INCLUDING A REHEATER SECTION, A CONDENSER, CONDUITS TO SUPPLY STEAM FROM THE BOILER SELECTIVELY THROUGH AN AHED FLOW PATH OR AN ASTERN FLOW PATH TO THE CONDENSER, THE AHEAD FLOW PATH INCLUDING THE HIGH PRESSURE TURBINE STAGE, THE REHEATER SECTION, THE INTERMEDIATE PRESSURE TURBINE STAGE AND THE LOW PRESSURE TURBINE STAGE, THE ASTERN FLOW PATH INCLUDING THE OR EACH REVERSE DRIVE TURBINE STAGE THE SAID TURBINE STAGES BEING MECHANICALLY CONNECTED TOGETHER, A PROPELLER SHAFT, A BOILER FEED PUMP AND AN ELECSTRIC GENERATOR BEING MECHANICALLY CONNECTED TO THE SAID TURBINE STAGES. 